1. Field of the Invention
The present invention relates to an image reading system including an illuminating means for illuminating an original and a reading means for reading image information of the original from light reflected from the original illuminated by the illuminating means while moving forwards and backwards.
2. Related Background Art
In a color image reading system for reading a color image of an original illuminated by an original illuminating lamp, a pre-scanning is generally performed prior to the substantial scanning in order to confirm a presence/absence of an original, an original size, an original position, original color information and the like.
In an image reading system used with a copier having a variable magnification function or in other apparatuses, a reading optical system for reading an original image to be copied is moved from a home position and accelerated to a motion speed suitable for a read magnification factor, and thereafter the original image is read while the motion speed is maintained unchanged. Most of such image reading systems adopt a stepping motor in view of cost and high precision position alignment.
In order for a stepping motor to drive a scanner at high speed and with low vibrations, it is essential to provide through-up and through-down of the motor. In order to read color information, it is necessary to read the color image at a constant speed and without vibrations. Accordingly, system design generally requires a preliminary drive period of the motor to attenuate vibrations generated during the through-up.
Notches or jags of a read image are formed by using a marginal step angle and drive torque of a stepping motor, the magnitudes of of which are based on the read magnification factor of an original. In most cases, jags can be suppressed by dividing a step angle of the stepping motor into micro-step angles by which the motor is driven.
During the pre-scanning, the original size and the like can be read even in an unstable state of the light amount of an original illuminating lamp. However, in reading original color information, it is necessary to perform the pre-scanning in a sufficiently stable state of the light amount. Prior to starting the pre-scanning read operation, it is therefore necessary to provide a stand-by period until the light amount becomes stable. The distance required for the through-up and through-down to suppress vibrations becomes longer as the motor drive speed increases. This becomes an obstacle against making the image reading system compact.
If a motion distance per one micro-step used for suppressing jags becomes nearly equal to a distance between original read lines, jags by a marginal drive torque become conspicuous. The shortest period of drive pulses is limited by a process time of control software of a microprocessor which drives a stepping motor. Therefore, even if a micro-step is used, the motion distance per one micro-step often becomes nearly equal to the distance between original read lines, and jags of a read image are likely to be formed.
It is an object of the present invention to provide an image reading system capable of shortening an original reading time and realizing a high speed reading.
In order to achieve the above object, according to one embodiment of the invention, there is provided an image reading system comprising: illuminating means for illuminating an original; reading means for reading an image of the original by using light reflected from the original illuminated by the illuminating means; moving means for relatively moving the reading means and the image in first and second directions, the first and second directions being opposite to each other; and control means for controlling to make the reading means read the image while being relatively moved by the moving means in the first direction, and to make the reading means read the same image while being relatively moved by the moving means in the second direction.
According to an another embodiment of the invention, there is provided an image reading method comprising the steps of: illuminating an original with illuminating means; reading an image of the original by using light reflected from the original illuminated by the illuminating means, by using reading means; relatively moving, by moving means, a relative motion between the reading means and the image in first and second directions, the first and second directions being opposite to each other; and controlling to make the reading means read the image while being relatively moved by the moving means in the first direction, and while being relatively moved by the moving means in the second direction.
The above configurations of the embodiments can shorten an original reading time and realize high speed reading.
The above and other objects, features, and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings and the appended claims.